Call super instead of returning nil for DateTime#<=>

The native DateTime#<=> implementation can be used to compare instances
with numeric values being considered as astronomical julian day numbers
so we should call that instead of returning nil.

Fixes #24228.

activesupport/CHANGELOG.md

@@ -1,3 +1,12 @@
+*   Rely on the native DateTime#<=> implementation to handle non-datetime like
+    objects instead of returning `nil` ourselves. This restores the ability
+    of `DateTime` instances to be compared with a `Numeric` that represents an
+    astronomical julian day number.
+
+    Fixes #24228.
+
+    *Andrew White*
+
 *   Add `String#upcase_first` method.
 
     *Glauco Custódio*, *bogdanvlviv*

activesupport/lib/active_support/core_ext/date_time/calculations.rb

@@ -165,13 +165,10 @@ class DateTime
   # Layers additional behavior on DateTime#<=> so that Time and
   # ActiveSupport::TimeWithZone instances can be compared with a DateTime.
   def <=>(other)
-    if other.kind_of?(Infinity)
-      super
-    elsif other.respond_to? :to_datetime
+    if other.respond_to? :to_datetime
       super other.to_datetime rescue nil
     else
-      nil
+      super
     end
   end
-
 end

activesupport/test/core_ext/date_time_ext_test.rb

@@ -354,6 +354,24 @@ class DateTimeExtCalculationsTest < ActiveSupport::TestCase
     assert_equal nil, DateTime.civil(2000) <=> "Invalid as Time"
   end
 
+  def test_compare_with_integer
+    assert_equal  1, DateTime.civil(1970, 1, 1, 12, 0, 0) <=> 2440587
+    assert_equal  0, DateTime.civil(1970, 1, 1, 12, 0, 0) <=> 2440588
+    assert_equal(-1, DateTime.civil(1970, 1, 1, 12, 0, 0) <=> 2440589)
+  end
+
+  def test_compare_with_float
+    assert_equal  1, DateTime.civil(1970) <=> 2440586.5
+    assert_equal  0, DateTime.civil(1970) <=> 2440587.5
+    assert_equal(-1, DateTime.civil(1970) <=> 2440588.5)
+  end
+
+  def test_compare_with_rational
+    assert_equal  1, DateTime.civil(1970) <=> Rational(4881173, 2)
+    assert_equal  0, DateTime.civil(1970) <=> Rational(4881175, 2)
+    assert_equal(-1, DateTime.civil(1970) <=> Rational(4881177, 2))
+  end
+
   def test_to_f
     assert_equal 946684800.0, DateTime.civil(2000).to_f
     assert_equal 946684800.0, DateTime.civil(1999,12,31,19,0,0,Rational(-5,24)).to_f